Pulse-width-modulation (PWM) amplifiers, also known as Class-D amplifiers, are a type of amplifier known for their relatively high efficiency in a variety of applications, e.g., amplification of an audio signal. Output stage power devices (typically metal oxide semiconductor field effect transistors, or MOSFETs) in a Class-D amplifier are operated as binary switches, i.e., they are either on or off.
In a Class D amplifier, ideally there are no switching losses, and the switches either have voltage across them but no current flow through them, or current flow through them but no voltage across them. Thus, ideally no heat is dissipated, and all of the power supplied to the Class D amplifier is delivered to the load, yielding theoretical power efficiency of 100%. In practice, non-ideal switching reduces the amplifier's efficiency.